Conventionally, an imaging device includes a diffuser plate configured by a lens array having a plurality of lenses that are arranged to be adjacent to one another. The diffuser plate uniformly diffuses light emitted from a light source.
In a case of the diffuser plate in which the respective lenses are regularly arranged in a grid pattern, use of a light source such as a laser diode for emitting coherent light to an imaging device causes interference of light passing through the lenses due to diffraction. This causes interference fringes. The interference fringes deteriorate uniformity of light intensity in the diffused light emitted to a subject.
Therefore, in order to suppress generation of the interference fringes in the diffused light, there is proposed, for example, a diffuser plate in which two or more kinds of lenses having different curved surfaces are disposed (for example, see PTL 1). As a result, uniform diffused light intensity is obtained.
However, the diffuser plate has a plurality of lenses. For this reason, when coherent light is emitted from the light source, interference fringes in the diffused light cannot be completely eliminated. As a result, an image that is obtained in a manner that an imaging element of the imaging device receives the diffused light reflected by the subject is occasionally affected by the interference fringes.